The present invention relates generally to a high-speed electrical interconnection. More particularly, the present invention relates to providing impedance matching between electrical circuits.
The increasing demand for high-speed voice and data communications has led to an increased reliance on optical communications, particularly optical fiber communications. The use of optical signals as a vehicle to carry information at high speeds is preferred in many instances. Advantages of optical media are, among others, higher bandwidth, greater immunity to electromagnetic interference, and lower propagation loss. In fact, it is common for high-speed optical communication systems to have signal rates in the range of approximately several gigabits per second (Gbit/sec) to approximately several tens of gigabits per second (Gbit/sec), and higher. However, although an optical communication system is useful for transmitting information at high speeds, optical signals ultimately have to be converted to electrical signals (and visa-versa, which are relatively high frequency electrical signals. As such, an electrical interface is required between the optical devices and any electrical devices.
One such structure used in high-frequency electrical applications is the multi-layer circuit board. Multi-layer circuit boards are often used in microwave, rf, millimeter wave, and other high-frequency applications. These structures offer the advantage of a reduced overall area, which facilitates attaining a desired degree of integration/miniaturization. Additionally, multi-layer circuit boards have been generally accepted in the high-speed communications industry because of their relatively low cost and high performance.
As is known, the isolation of signal lines and impedance matching are important characteristics of an electrical interconnect. To wit, the electrical interconnection must foster the isolation of signals, and must foster impedance matching, if it is to offer high performance. That this end, poor isolation between signal lines can result in undesired cross-talk. Moreover, poor impedance matching between signal lines can result in undesired back reflections, and may ultimately affect performance due to increased insertion losses, for example.
Conventional high-speed connectors, namely RF connectors such as SMA-type connectors, have been used to improve impedance matching. Although such an interconnection scheme may provide good performance in high frequency electrical applications, it does not allow for sufficient freedom in attaining higher degrees of integration/miniaturization.
It is an object of the present invention to provide an electrical interconnect having a multi-layer circuit board structure, wherein the source and load impedances are substantially matched.
It is a further object of the present invention to provide an electrical interconnect for two high speed signal lines which may be one two different multi-layer circuit boards.
To achieve these and other objects, the electrical interconnect includes a signal line that vertically connects a first transmission line extending along the surface of one of the layers of the multi-layer circuit board structure to a second transmission line extending along the surface of another of the layers of the multi-layer circuit board structure, an electrically conductive spacer that substantially circumferentially surrounds the signal line, and a dielectric medium interposed between the signal line and the electrically conductive spacer. The electrical interconnect thus has a structure resembling a coaxial transmission line, in the vertical (thickness) direction of the multi-layer circuit board structure.
The desired characteristic impedance can be provided by selecting appropriate dimensions for the electrically conductive spacer, and by providing a medium having a given dielectric constant around the signal line.